Bombs and missiles which are deployed from aircraft typically include guidance fins or wings for controlling flight after release from the aircraft. Space considerations on the aircraft typically require that the fins be folded in a stowed position while being carried on the aircraft. This is naturally of more concern with larger bombs. Folded fins, of course, create the need for a mechanism to deploy the fins upon release from the aircraft.
One class of known mechanisms includes electrical or squib devices for retaining and deploying fins. Another known device includes a band that wraps around an outer edge of the stowed fins and individual deployment springs that act on the fins when the band is released.
The conventional mechanisms suffer from deficiencies. The electrical and squib devices are effective with smaller fins, but are less effective with larger fins because of the dynamics involved in deploying larger fins after release from a moving aircraft. The wraparound band and spring devices have problems related to the complexity of the structure. The band includes a subassembly of small parts that can become loose and damage the aircraft (for example, by being sucked into the engine) when the band is released. In addition, the individual springs for driving the fins to the deployed position must work simultaneously. A weak or broken spring could cause a failure to deploy a fin or cause late deployment of a fin, either of which could result in an adverse flight response. Adverse flight of a bomb or missile could, among other things, turn the bomb into the aircraft flight path, which poses a serious danger to the aircraft.
The invention provides an apparatus for retaining fins in stowed position and deploying the fins upon release from an aircraft that eliminates the problems in the art.
The invention includes a single device that both retains the fins in the stowed position, and with spring power, acts to cause the fins to pivot from the stowed position to the deployed position. Thus, the number of parts and the complexity of the device are reduced, compared to the known art. In addition, no part of the apparatus according to the invention becomes loose or free, and there is therefore no danger of flying parts damaging the aircraft or engine.
According to the invention, the device for retaining and deploying fins includes a yoke mounted for sliding axially on a shaft. The yoke is positioned at a radially central location at a missile or bomb tail to engage edges of the pivotally mounted fins that are inwardly facing in the stowed position. A drive spring is mounted between a fixed support and the yoke. When released, the drive spring drives the yoke along the shaft. The yoke pushes against the fins, causing them to pivot from the stowed position to the deployed position. The drive spring is selected to store a sufficiently high amount of energy to overcome inertia in the fins and air resistance working against pivoting, thus ensuring deployment of the fins.
The yoke is conveniently shaped as a cup-like member mounted on the shaft, with the drive spring disposed around the shaft in the cup interior, which helps maintains the linear orientation of the components during deployment. Linear movement of the cup is translated to pivoting movement of the fins by the yoke pushing each fin at an engagement point located a distance from the fin pivot point.
According to a preferred embodiment of the invention, the fins each include a tab extending from the inwardly facing edges. The yoke includes radially extending arms at a first end and a radially extending ring spaced from the arms, the area between the arms and the ring defining an engagement space for the tab. The tabs are received in the space between the arms and the ring, and are prevented from pivoting and thus retained in the folded position by the ring. The arms push on the fin tabs when the yoke is driven by the spring to cause the fins to pivot.
According to another aspect of the invention, a mechanism for releasably retaining the yoke in the stowed position includes a plurality of balls disposed in holes in the spring shaft and bearing on the end of the cup. The balls prevent the cup from moving relative to the spring shaft. The balls are retained in position in the holes by a retaining pin disposed inside the spring shaft. The retaining pin includes recesses for receiving the balls when the pin is moved to a release position.
A retaining spring is disposed in the spring shaft for driving the retaining pin to the release position. A lanyard extends through aligned holes in the spring shaft and retaining pin to hold the retaining pin against the retaining spring. When the lanyard is withdrawn, the retaining spring drives the retaining spring to the release position, which allows the balls to drop into the recesses and no longer bear on the cup. The cup is then free to move under power of the drive spring to deploy the fins.
The use of the retaining pin and spring arrangement provides a mechanical advantage in retaining the yoke cup against the drive spring with the balls and retaining pin, and consequently, requiring movement of the pin to release the yoke, which requires a much smaller force than needed for the drive spring. The lanyard holding the retaining pin in place is thus under a greatly reduced force. Release of the cup for deploying the fins thus requires less force as the lanyard is pulled out against the force of the retaining spring, which is lower than that of the drive spring.